Power supplies are widely used in many applications to adapt an input power signal in a standardized form with rated voltage and frequency to the particular output signal form needed by the application. For example, the mains power signal has a rated a.c. voltage between 100-240 volts and a frequency of 50/60 Hz (i.e., input at "high" voltage). Computers often internally require d.c. voltages of 5 and 12 volts (output at "low" voltage). Other applications, such as energy-saving lighting devices require voltages of several hundreds of volts.
There is a huge demand to provide inexpensive electronic circuits for the power supplies. The circuits should be minimized in their physical dimensions and, if possible, integrated on monolithic semiconductor substrates. To guaranty substantially constant output voltages of the power supply, control signals from the "low" circuit voltage portions to the "high" voltage circuit portions, or vice versa, are often used. Between portions with substantially different voltages, provisions are required to (a) transfer or exchange control signals and (b) substantially isolate the portions. These are sometimes conflicting requirements.
For example, in some power supplies, semiconductor switches (e.g., bipolar transistors, MOSFET transistors, thyristors), alternatively pull a node to a high end (i.e. d.c. 700 volts, rectified input voltage) and to a zero voltage line (half bridge arrangement). Then, the resulting rectangular voltage is down-transformed and rectified to a low output voltage. Preferably, the semiconductor switches are controlled by signals derived from the low output voltage. A switch driver should provide (a) transfer of control signals from the output to the semiconductor switches and (b) isolate high and low voltage portions. This is especially important for that portion of the driver which controls the switch at the high end. In other words, high and low voltage portions are floating with no reference to other. This requires, for example, space, packages, extra lead wires, etc. and is therefore not wanted.
It is known in the art to have driver circuits with floating regions integrated on a single monolithic chip together with non-floating regions. UK Patent Application 2310081 published Aug. 13, 1997 discloses a level shifting high voltage device for electrically coupling a subcircuit with a higher, floating voltage to a subcircuit with a lower voltage.
The integration of floating regions and isolation regions into monolithic integrated chips can require additional manufacturing steps (sometimes epitaxy) which are not wanted (time, resources, etc.).
Therefore, the present invention seeks to provide semiconductor structures for driver circuits and manufacturing methods which mitigate or avoid these and other disadvantages and limitations of the prior art.